Post etch photoresist and residue removal is a critical step in semiconductor processing. If a cleaning method is inadequate, remaining residue on one or more parts of a semiconductor device such as a semiconductor wafer can lead to problems with film quality, inadequate adhesion of subsequent layers, or diffusion contamination in subsequent processing steps. For example, during a metal etch, polymer and metal byproducts may be formed which must then be removed. Unwanted byproducts of etch processes include hydrocarbons, oxides, silicon and silicon-containing materials, and organometallic compounds.
Wet cleaning or dry plasma processes may be used to remove unwanted residue. Previously developed dry plasma cleaning processes use, for example, combinations such as O2/forming gas (FG)/CF4, O2/H2O/C4 and FG/H2O/CF4. (Forming gas denotes a nitrogen/hydrogen gas combination). Previously developed wet cleaning processes use, for example, amine-based solvents such as Ashland Specialty Chemical Company's ACT series or EKC Technology, Inc.'s EKC series. Alternately, strong acids such as 50:1 HF or 90% H2SO4/10% H2O2 (hot Piranha) are currently used for post etch cleans.
However, the previously developed processes have a number of drawbacks. Typically, wet clean processes use strong chemical solvents or acids, often for a significant length of time. For example, times as long as twenty minutes may be required to perform a post metal etch wet clean process with an amine-based solvent. Further, because of the aggressive cleaning chemistry and the length of time used, metal structure degradation can occur. Special handling of aggressive chemical agents may add to the cost of the post-etch cleaning process as well.
Previously developed plasma cleaning processes have drawbacks as well. For example, using a fluorine-containing plasma to perform a post metal etch clean can leave either fluorine atoms or fluorine-containing molecules on the surface or sidewall of the device structures. The fluorine may become embedded in the surface over time. Subsequent wet cleaning using, for example, deionized water, removes the embedded fluorine, leaving behind surface and sidewall pits. The amount of surface pitting is directly proportional to the fluorine content in the post metal etch clean process.
Therefore, it is desirable to provide a cleaning process that effectively removes unwanted byproducts, but does not cause significant structural damage to a semiconductor device.